Method for stabilizing soybean oil refined by solvent treatment



Dec. 29, 1953 FASSINO METHOD FOR STABILIZING SOYBEAN OIL REFINED BY SOLVENT TREATMENT Filed Oct. 2, 1948 INVENTOR. HERBERT J. FASSINO ATTORNEYS there is a propane inlet `of the reflux liquid to `perature gradient method alone n U liquefying pressure (about 615 pounds per square inch gage), the composition of extract and raffinate radically shifts; under equilibrium conditions, most of the soybean oil is now in the raffinate. By selecting the appropriate temperature within the range between the temperature of maximum miscibility of the oil and propane and the critical temperature of the oil-propane mixture, almost any desired fractionation can be accomplished. Although this fractionation can be achieved in a batch process, it is much more satisfactory both from the standpoint of accuracy and commercial practicability to carry out the fractionation continuously in a vertical fractionation tower in which the propane and oil are countercurrently contacted. A particularly satisfactory form of such a tower is one in which and a raffinate phase outlet at the bottom, an extract phase outlet and reflux inlet near the top, and a charge oil inlet in the middle portion. In such a tower solvent flowing upwardly from the solvent inlet dissolves most of the oil flowing downwardly from the charge oil inlet; raffinate phase accumulates in the bottom of the tower and the extract phase is continuously withdrawn from the extract phase outlet at the top; the solvent content of the extract phase is reduced and some of it is returned .to the tower through the reflux inlet and flows downwardly in countercurrent contact with the upflowing extract phase; in this contactwbetween downflowing reflux liquid and upiiowing extract phase, the latter tends to become enriched in the more soluble oil components and to precipitate less soluble oil components, a process well known to those familiar with the art of solvent frac'- tionation and fractional distillation as rectification. In solvent fractionation under paracritical conditions the entire tower may be at a single temperature in the paracritical range and reflux liquid introduced through the reflux oil inlet may be the sole means of rectifying the extract phase. However, it is also possible to rectify the extract phase by establishing a temperature gradient within the upper part of the fractionation tower so that the temperature increases with increasing'elevation; under these conditions, a larger fraction of the oil than is required is at first dissolved into the extract phase but precipitation -occurs as it flows upwardly to regions of higher temperature until only the desired fraction, remains in the extract phase withdrawn at the extract phase outlet. The liquid precipitated by the upowing extract phase serves as reflux liquid las it flows downwardly through the fractionation tower. Rectification of the upflowing extract phase may be accomplished by either the return the tower or by thetemor by both methods used simultaneously.

Although a fraction comprising almost any desired proportion of the charge oil may be obtained by control of the paracritical temperature, refluxing, solvent ratio, etc., control of the chemical composition of the fractions is limited to sortingr out the more soluble from the less soluble components so that it may happen, as in the case of soybean oil, that two components which it would be desirable, for commercial reasons, to keep together are separated into the two different fractions. In soybean oil rening, it is desirable to eliminate the color bodies, phosphatides, fatty acids and certain constituents present in minute quantity which cause bad taste or odor. As de*- scribed in my copending application Serial No.

at 699,320, this is very successfully done by propane fractionation and steam treatment. However, the clear, odorless, and sweet tasting oil produced by this process has lost some of the natural preservatives which are present in the crude oil. These substances are present in the crude oil in a very small percentage but are extremely effective in protecting the oil from oxidation by the air; from polymerization, conjugation, etc., under the influence of heat; and in general, from any reaction which tends to slowly degrade the oil upon standing, especially in the presence of air or under temperatures slightly above usual room temperatures. The precise nature of these inhibiting substances is not known but there appears to be several of them having a variety of inhibiting effects. They will all be referred to herein as stabilizing agents; this term includes particularly but not merely antioxidants; it also includes other components which prevent degradation due to polymerization, conjugation and the like. All methods of refining involve the loss of some of these stabilizing agents, and although the refined oil may be satisfactory for many commercial purposes, the present invention provides a means for producing a refined oil of superior stability. For example, refined oils may be subjected to an oven test in which they are stored at a temperature of F. for several days; all refined oils eventually deteriorate in taste, apparently as the result of oxidative deterioration, but the deterioration is markedly slower in the case of oils refined by the method herein disclos-ed. This method is based upon the discovery that stabilizing agents from a crude oil tend to concentrate in the rainate from a propane fractionation, and that the refined oil obtained from the extract phase can be made unusually stable by the addition of a small portion of the raffinate. Naturally, some of the undesirable color bodies and other impurities are thus returned to the oil, but so small a quantity of raffinate is required in order to endow the refined oil with optimum keeping qualities that the disadvantages are not serious. Excellent stability can usually be achieved by adding about one-tent of the railinate, without further treatment, to the refined oil. Refined oil is darkened slightly by such treatment; but the ramnate may be treated and washed with such solvents as acetone and alcohol, to obtain a precipitate which is a light tan and which may be added, in whole or in part, without visibly effecting the color or clarity.

Among the stabilizing agents are some which have been found to be so sensitive to heat that they darken the oil if present therein during steam stripping. It is an advantage of the present invention that the extract fraction, which comprises almost all of the crude soybean oil may be subjected to extensive steam stripping after the heat sensitive stabilizing agents have been separated by propane fractionation and before any of them have been returned to the oil from the fractionation raffinate. Steam treatment of the extract not only removes the last traces of the propane solvent but also eliminates volatile impurities such as the lighter fatty acids, and certain impurities which adversely affect taste and color. For six hours with ten per cent steam .at temperatures as high as 475 F. steam stripping may be carried out with only beneficial effects. The resulting oil is better' tasting and slightly clearer in color than before the stripping operation. A small quantity of .the stabilizing agents menne-s1 .may thenvbe; adde'd'stoltheiil'it ipro'ductofisuperiorduality.

".The :accompanying :drawing shows cdiagram :fanaticallyfaareningsystem employingrthemethod o produce '.:arefined of the presentfinvention. .Crudeisoybeanoiliis 11 chargeduthrough llin-e |50 ato-.aecontinuous-counter- @currentfraetionationftower Ir' I :infwhichit isiractionaltedtwith thefpreferred? solvent, propane, :.in- `troduced to fthe 'lower :end :of .tower .I,I ithrough line i I 2. Withinthe '.t'ower, .f pre determined iperatfcriticalf conditions-are maintained by .controlling tlre temperature fand :pressure Lof .the oil .zand propane charged, :and :also byl heatingLmeans :lf3 ean'drefluxing means ZIA.y v:In theipresentsexam- .mixtureiintofaeseventyevexper cent 'extractaphase an'difastwentyevezperfcentrafnatephase. :The ra'inate phasefinztower, I I .isxpumped' by .pnmpt through .line IB and heat-'er IITI `to iafsecond scontinuous countercurrent fractionation @tower I8 :supplied with additional vpropane through .line -1'I9. 'llnfsecondtower VI8 the ranateisfractionated I under `'slightly dilerent vparacritical .condiitions `to obtain ..an overhead .at 11.20 comprising V'about itwenty=three iper-:cent .of the loriginal crude l ffil, and .a .dark jelly ranate. at 2 I I comprising abo'ut two:l percent ofthecrudegoil. rThe purpose rof the :two :tower .fractionation in :the example "di'sclosedsisrfto .Lobtain 'from fthe lrraw soybean foil mfractionfcomprised'offthe relatively more saturated: glyceridessuitable for.u foodf purposes (i. re. seventy-five iper :cent extract from :tower :I I i, andfafraction of. relativelyunsaturated.glycericles :mostfsuitable I4fori paint drying mils, (i. 'e.'the I,twenty-thr.ee:;per `centaextraot:takenz'fronri ztower 5158).. v-Cl'lms-ztwo:diiferentrenedioils arezo'btained.

Ordinarily the paint oil doesnotzrequire reddi- 'Ltional treatment. IfA no upaintfoil; fraction is. 'clelfsireid, monlyone :tower: neednbe" operated, and the ioverhead eXtractmay containbetweerrninety` and :ninety-nine per :cent of` the "crudeaoil; or both tower II fand' tower I8 mayzbe employedand the utwooverheadsmixed by openingvalve 22;" this ftype of operation employs the two .towers 'to rachieveone tower operation; someiaidvantage'is .-gained `lin .that a satisfactory Yfractionation:is

-accomplis-hed `with somewhat less propane.

The food-'oil fraction (either the overhead from Ytower I Igor both the: overhead of tower i I I "and tower I8, iffnoaint oil fraction :..fisdesirew .is .t-ransferredthrough line 23 to be 'diverted by v.valves 214 and y25v-either to treatment jfor salad fand cooking oil` purposes, tor to treatment to produce a margarine orshortening. i In .the former vcase, th'egoilis subjected. to thefsteam stripping process referred to in the trade assteam deodor- -ization by .-:cnventinnal ksteam deodozation means 26. The deodorized salad and cooking oil i is fwithdrawnithroughdine 2f'kafterttheraidition 7of iazsmall quantity fofista'bilizing `agents .obtained .iniasmanner describedihereinafter. vrgarine or shorteningxis iprorluced Vbyhydrogenationfat 28 followedby."steamfdeodcrizationsats, fanditheadilitionffofsstabilizingagentsgto vprovince vthe?nishedsproduct-:at:31|).

:The stabilizing agents '.arexprefera'bly A,Obtained 1 from the :raffinate withdrawn 1 .through etower t8 to line ..21 rbyz'rstffsnbjecting;itttomcetonei-extracf :tionat 31 to4 separate.: itainto acetonefsolblese :and acetone insolubles A353. @,'The cacetone .insoluibles usually comprise about italo-:thirds .fof the ttreatedcranate .The acetoneinsolubleoareinext Vwashed or :extracted rwith.I alcohol A:an aalcohol yextraction step 314, wand separated finto i; alcohol 'solubles 35 'andfalcoholinsolubles "3.6. 'imhoalcohol insolubles twill 1 usnally'f:befoundz` to fcontain;` sum- '.cient stabilizing agents A'and 'i very. little coloring imatter, and may s be `.transferred through vlines 37, 33 :and .f3.9 :to the .;oi1 sorrshortening .;oflines `2'! and :30 respectively. .fS-ometimes :ovenitestsoof products :obtainedifrompparticular oils mavtssug- `gest the desirability of `vreturningtthe `.greaterrportion 'fthe raffinate:stabilizingzagentsztotthezfrened` oil. 'A smallfouanttyrof :untreated traninate, or of acetone:insolublestwhich:hasfnotxbeen alcohol treated yimay zibe zadded'fto; the: rennen?v oil and .a4 I "respectivelvrwhen the: resultsv demonstrate? theades'ira-bility :of ynain-g aso.

Typical process conditionsforzzreflningrsoybean oil nin 'accordancewwth the presentnnethodeare given herewith:

'Tower' height overall j60j'ft.

kStrilolzier j Notless"than10t.

"Reoti-er L NotI less than'mft, Reux ratio v 5016-018. Temperature gradient L" 5" F. "(r ectier), Final 1 stripping quivalent tot? hours, 3% gsteamhr. ,jat '52 He abs-.142.5

In :a typical .Single tower.;operation minet-weight v percent of .theoil isi taken overheadiandsthe :two per cent ralnate is treated with acetone to obtain acetone insolubles; acetone insolublesamolmting to about one-tenthfof onegperreentzoftthe original "oil is then addedtto:thefrenedzioil: aftercsteam stripping.

The effect'of` adding `various portions from'the bottoms fraction -before `-andgafter vsteam'treatment :is shown-inthe following-,charm Tabla-#Processing of "soi/bean' 4oil v vSolexol 90% overhead TASTEFSCORE `l0=ifreshly deodorized cottonseed oil T 9=57"reverted soya 8='1f)% reverted soya ".`5i'5=25% reverted soya 3=50% reverted soya (if-400% revertedsoya 'phases respectively;

a ketone solvent to form The stabilizing effect can be accomplished in `some degree with an unselectd portion of the raiiinate; however, much better results follow from treating the raiiinate to obtain a selected portion which contains a concentrate of the stabilizing agents and a minimum of color bodies. In the example, acetone insolubles or, more broadly, ketone insolubles are employed. There are other methods of obtaining a satisfactory selected portion of the raiiinate, however. It has been found that a concentrate of stabilizing agents may be separated from the raffinate by chilling the raiiinate in the presence of a solvent diluent such as hexane or propane; the extent of chilling necessary to obtain a suitable stabilizing agent fraction will vary from oil to oil, and a sample must be tested in order to determine just how much of a precipitate should be chilled out; chilling temperatures generally fall in the range between F. and 40 F. Another method of treating soybean oil rainate to obtain a concentrate of stabilizing agent involves contacting the raihnate with an equeous caustic solution and washing the remaining mixture with water to separate an oil scum from the water soluble constituents; the oil scum is found to contain a concentrate of stabilizing agents.

One of the advantages of the present process is that it makes possible extensive steam treatment of the soybean oil when it is in its intermediate condition after decolorization but before addition oi stabilizing agents. In this intermediate condition the oil is generally steam in a temperature range between 350 F. and 450 F. for a period of between one and ve hours with between ve and twenty per cent of steam under a vacuum oi" between two and twenty mm. of mercury to strip it of volatile components.

It is, of course, possible to subject the stabilizing agent portion of the raffinate to various decolorizing treatments in order to reduce to a mnimum the coloring effects of adding it to the refined soybean oil. For example, this portion may be contacted with a clay or activated charcoal; or it may be chemically treated with such bleaching agents as chlorine dioxide, hydrogen peroxide, etc.

I claim:

l. A method of rening soybean oil which includes the steps of: intimately contacting said soybean oil with a solvent having a critical temperature of less than 450 F. under liquefying pressure and in the paracritical range of the solvent-oil mixture to form extract and raffinate phases, said rainate phase containing less than ten per cent of said oil; separately recovering extract and raiinate from said extract and raffinate treating said raffinate with a precipitate containing stabilizing agents; and adding a portion of said precipitate to said extract.

2. A method of rening soybean oil which includes the steps of: intimately contacting said soybean oil with a solvent having a critical temperature of less than 450 F. under liquefying pressure and in the paracritical range of the solvent-oil mixture to form extract and rafnate phases, said raffinate phase containing less than ten per cent of said oil; separately recovering extract and rainate from said extract and raflinate phases respectively; treating said a ketone solvent to form a precipitate containing stabilizing agents; separating said precipitate and treated with raffinate with washing it with additional solvent selected from a group consisting of alcohols and ketones until additional washing produces no substantial lightening in color; and adding a portion of said washed precipitate to said extract.

3. A method of refining soybean oil which includes the steps of intimately contacting said soybean oil with a solvent having a critical ternperature of less than about 450 F. under liquefying pressure and in the paracritical range Yof the solvent-oil mixture to form extract and rainate phases, said raffinate phase containing less than ten per cent of said oil; separately recovering extract and raflinate from said extract and raffinate phases respectively; treating said raffinate with ketone solvent to form a precipitate containing stabilizing agents; separating said precipitate and washing it with an alcohol; and adding a portion oi said washed precipitate to said extract.

4. In the method oi refining crude soybean oil which involves intimately contacting said oil with a solvent having a critical temperature of less than 450 F. under liquefying pressure and in the paracritical range of the solvent-oil mixture to form an extract phase containing substantially all of said oil and to precipitate a small ranate phase containing substantially all color bodies and phosphatides, the improvement which includes the steps of: recovering decolorized soybean oil from said extract phase and treating said extract with steam to strip it of volatile components; treating the rainate with an aqueous caustic solution and washing the remaining mixture with water to separate an oil scum from the water soluble constituents; and adding at least a portion of said oil scum to said steam treated soybean oil extract.

5. In the method of refining crude soybean oil which involves intimately contacting said oil with a solvent having a critical temperature of less than 450 F. under liquefying pressure and in the paracritical range of the solvent-oil mixture to form an extract phase containing substantially all of said oil and to precipitate a small ranate phase containing substantially all color bodies and phosphatides, the improvement which includes the steps of recovering decolorized soybean oil from said extract phase and treating said extract with steam to strip it of volatile com'- ponents; treating said raiinate with a ketone solvent to form a precipitate containing stabilizing agents; separating said precipitate and washing it with additional solvent selected from a group consisting of alcohols and ketones until additional washing produces no substantial lightening in color; and adding a portion of said washed precipitate to said extract, said portion comprising less than one-tenth of one per cent of the original oil.

6. In the method of refining crude soybean oil which involves intimately contacting said oil with a solvent having a critical temperature of less than 450 F. under liquefying pressure and in the paracritical range of the solvent-oil mixture to form an extract phase containing substantially all of said oil and to precipitate a small raffinate phase containing substantially all color bodies and phosphatides, the improvement which includes the steps of recovering decolorized soybean oil from said extract phase and treating said extract with steam in the temperature range between 350 F. and 450 F. for a period of between one and ve hours with between ve and twenty per cent of steam under a vacuum of between two and twenty mm. of mercury to strip it of volatile components; treating said raiiinate with a ketone solvent to form a precipitate containing stabilizing agents; separating said precipitate and Washing it with additional solvent selected from a group consisting of alcohols and ketones until additional Washing produces no substantial lightening in color; and adding a portion oi said Washed precipitate to said extract, said portion comprising less than one-tenth of one per cent of the original oil.

'7. A method as described in claim 11 in which said bleaching agent is clay.

8. A method as described in claim 11 in which said bleaching agent is chlorine dioxide.

9. A method of refining soybean oil which includes: intimately contacting said soybean oil With a solvent having a critical temperature of less than about 450 F. under a liquefying pressure and in the paracritical range of the solventoil mixture in which the miscibility decreases as temperature increases, to form an extract phase containing most of the oil and a relatively small raffinate phase containing most of the color bodies from said soybean oil; separately withdrawing said extract and ranate phases; returning not more than one tenth of said rafnate to said extract oil to produce an oil which is at least nine tenths decolorized and contains at least a portion of each raiiinate stabilizing agent.

l0. A method of refining soybean oil which includes: intimately contacting said soybean oil with a solvent having a critical temperature oi less than about 450 F'. under a liquefying pressure and in the paracritical range of the solventoil mixture in which miscibility decreases as temperature increases, to form an extract phase containing most of the oil and a relatively small rafnate phase containing most of the color bodies from said soybean oil; separately withdrawingiii said extract and raiiinate phases; separately treating the extract oil of said extract phase with steam to strip it of volatile components; dividing said rafiinate into major and minor parts, said minor part amounting to less than one tenth of said raffinate; and adding said minor raiiinate portion to said extract oil after said extract oil has been steam treated.

11. A method of reiining soybean oil which includes: intimately contacting said soybean oil with a solvent having a critical temperature of less than about 450 F. under a liquefying pressure and in the paracritical range of the solventoil mixture in which miscibility decreases as temperature increases, to form an extract phase containing most of the oil and a relatively small raffinate phase containing most of the color bodies from said soybean oil; separately withdrawing said extract and raiijnate phases; treating at least a part of said raffinate with a bleaching agent to lighten its color; and adding at least a part of said bleached raffinate to said extract oil.

HERBERT J. PASSING.

References Cited in the le 0f this patent UNITED STATES PATENTS OTHER REFERENCES Chemical & Engineering News, vol. 24, December 10. 1946; page 3188. 

9. A METHOD OF REFINING SOYBEAN OIL WHICH INCLUDES: INTIMATELY CONTACTING SAID SOYBEAN OIL WITH A SOLVENT HAVING A CRITICAL TEMPERATURE OF LESS THAN ABOUT 450* F. UNDER A LIQUEFYING PRESSURE AND IN THE PARACRITICAL RANGE OF THE SOLVENTOIL MIXTURE IN WHICH THE MISCIBILITY DECREASES AS TEMPERATURE INCREASES, TO FORM AN EXTRACT PHASE CONTAINING MOST OF THE OIL AND A RELATIVELY SMALL RAFFINATE PHASE CONTAINING MOST OF THE COLOR BODIES FROM SAID SOYBEAN OIL; SEPARATELY WITHDRAWING SAID EXTRACT AND RAFFINATE PHASES; RETURNING NOT MORE THAN ONE TENTH OF SAID RAFINATE TO SAID EXTRACT OIL TO PRODUCE AN OIL WHICH IS AT LEAST NINE TENTHS DECOLORIZED AND CONTAINS AT LEAST A PORTION OF EACH RAFFINATE STABILIZING AGENT. 